1. Field of the Invention
The present invention relates to the field of angioplasty. In particular, the present invention relates to a method of purging a dilatation balloon catheter.
2. Description of the Prior Art
Angioplasty has gained wide acceptance in recent years as an efficient and effective method for treating types of vascular diseases. In particular, angioplasty is widely used for opening stenoses in the coronary arteries, although it is also used for treatment of stenoses in other parts of the vascular system.
The most widely used form of angioplasty makes use of a dilatation catheter which has an inflatable balloon at its distal end. Using fluoroscopy, the physician guides the catheter through the vascular system until the balloon is positioned across the stenosis. The balloon is then inflated by supplying fluid pressure through an inflation lumen to the balloon. The inflation of the balloon causes stretching of the artery and pressing of the lesion into the artery wall to reestablish acceptable blood flow through the artery.
Before a dilatation catheter is used in an angioplasty procedure, the balloon and catheter must be purged of any air to prevent the possibility of air entering the vascular system. The purging of air from the balloon and catheter with radiopaque purging/inflation fluid also presents the advantage of making the catheter more visible under fluoroscopy. Typically, purging of the catheter can be accomplished either by a distal venting device, as in U.S. Pat. No. 4,638,805, or via the provision of two separate lumens to the balloon. In the latter case, one lumen is used to introduce liquid into the catheter and balloon and the second lumen is provided to allow the purged air to escape, as in U.S. Pat. No. 4,323,071. The purging lumen may be permanently incorporated into the catheter or may be removable after purging. A disadvantage of these purging methods is the requirement of two separate lumens.
In order to treat very tight stenoses with small openings, there has been a continuing effort to reduce the profile (and shaft diameter) of the catheter so that the catheter cannot only reach but also cross very tight stenoses. A successful dilatation catheter must also be sufficiently flexible to pass through tight curvatures through the very tortuous path of the vascular system. A further requirement of a successful dilatation catheter is its "pushability".
This involves the transmission of longitudinal force along the catheter from its proximal end to its distal end so that a physician can push the catheter through the vascular system and the stenosis.
Two types of dilatation catheters are "over-the-wire" catheters and "non-over-the-wire" catheters. An over-the-wire catheter is one in which a separate guide wire lumen is provided so that a guide wire can be used to establish the path to the stenosis. The dilatation catheter can then be fed over the guide wire until the balloon is positioned within the stenosis. One problem with the over-the-wire catheter is the requirement of a larger profile (and shaft) in order to allow for the separate guide wire lumen.
A non-over-the-wire catheter acts as its own guide wire, and thus there is no need for a separate guide wire lumen. One advantage of a non-over-the-wire catheter is its potential for reduced profile (and shaft) since a guide wire lumen is not required. However, one disadvantage is the inability to maintain the position of the guide wire within the vascular system when removing the catheter and replacing it with one of a smaller (or larger) balloon diameter. Thus, with the non-over-the-wire catheter, the path to the stenosis must be reestablished when replacing the catheter with one having a different balloon diameter.